Chest Trauma
Coauthored with David Dries, MD
KEY POINTS
1 Victims of chest trauma who survive to hospital admission have a generally good prognosis and generally do not require thoracotomy; rib and sternal fractures and pulmonary contusions are the most common injuries.
2 Ensuring that the airway is patent and respiratory drive is adequate is critical first step. Securing adequate venous access and draining pneumothoraces or hemothoraces are the next priorities.
3 In the setting of thoracic trauma, hypotension is due to hemorrhage unless proven otherwise. If the neck veins are flat, hemorrhage is most likely; if the neck veins are distended, cardiac tamponade, tricuspid valve disruption, and tension pneumothorax are leading candidates. Classic symptoms, however, are frequently absent. Myocardial dysfunction secondary to blunt cardiac injury or infarction should always be considered.
4 Tracheobronchial injury should be suspected when hemoptysis or a large bronchopleural fistula is present. Early evaluation by bronchoscopy is indicated and the injured lung may be excluded by a double-lumen intubation.
5 Hemothorax, widening of the mediastinum, an arm/leg pulse or blood pressure deficit, thoracic inlet hematoma, and multiple rib or sternal fractures serve as clues to major vascular injury. Patients with these signs should be evaluated by CT angiography in a setting where endovascular therapy and immediate thoracotomy are immediately available.
6 Abdominal compartment syndrome, an often subtle consequence of both surgical and external trauma and resuscitation, can impair pulmonary and renal function. Visceral hypoperfusion precipitates metabolic acidosis vascular collapse unless rapidly decompressed by laparotomy.
▪ EPIDEMIOLOGY
Almost 500,000 Americans suffer chest trauma each year, accounting for approximately 20% of all hospital-treated injuries. Chest injuries directly result in 20% to 25% of all trauma deaths and may contribute significantly to mortality in another quarter of them. The chest wall, pleural space, and lungs are involved in the great majority of chest injuries (Table 35-1). Although serious burns, crush injuries, and gunshot wounds account for considerable morbidity, in most cases the wounds are nonpenetrating and result from a misadventure involving a motor vehicle. When a vehicular accident proves fatal, more than one half of the deaths are directly attributable to severe thoracic trauma. Most deaths occur at the scene of the accident as a result of a catastrophic, unsalvageable injury, such as aortic transection or massive neurological injury. Fortunately, most patients who live long enough to be transported to a hospital will survive. Until the past quarter century, this was not the case; dramatically improved survival of seriously injured patients has accompanied their care in specialized intensive care environments.
▪ MECHANISMS OF CHEST TRAUMA
Penetrating Chest Injuries
Knife and gunshot wounds account for the majority of penetrating chest injuries. Of these, knife wounds tend to be more survivable, as their damage is usually confined to a limited area. The injury caused by a gunshot wound depends not only on the path of the bullet, but also on the energy delivered per round, the number of impacting rounds, and the characteristics of the projectile (solid point vs. hollow point). Although the path taken by the projectile can be inferred from the entrance and exit wounds, the trajectory may be altered by ricochet off bony structures, and the damage tract may be
much wider than the narrow tract of the missile itself because of the wide-ranging explosive effect that accompanies passage of the high-speed bullet through tissue. Moreover, depending on the phase of the respiratory cycle during which entry occurred, a bullet may traverse the diaphragm to injure the high abdominal structures even when entrance and exit wounds align above the costal margin. Bullet wounds below the margin of the scapula posteriorly and below the nipple anteriorly must be considered to involve both the chest and abdomen. Computed tomogram (CT) scanning has replaced endoscopy and vascular constrast studies as the imaging modality of choice in the setting of penetrating and blunt thoracic trauma. Endoscopy and vascular studies play a secondary role after screening CT evaluation but frequently are no longer required. CT scanning can be particularly valuable when a projectile is suspected to traverse the mediastinum. Tracks of stab wounds and gunshot wounds can be followed with CT imaging. Though CT imaging has improved our ability to identify injury to the diaphragm, operative examination remains the “gold standard” for this specific component of the evaluation.
much wider than the narrow tract of the missile itself because of the wide-ranging explosive effect that accompanies passage of the high-speed bullet through tissue. Moreover, depending on the phase of the respiratory cycle during which entry occurred, a bullet may traverse the diaphragm to injure the high abdominal structures even when entrance and exit wounds align above the costal margin. Bullet wounds below the margin of the scapula posteriorly and below the nipple anteriorly must be considered to involve both the chest and abdomen. Computed tomogram (CT) scanning has replaced endoscopy and vascular constrast studies as the imaging modality of choice in the setting of penetrating and blunt thoracic trauma. Endoscopy and vascular studies play a secondary role after screening CT evaluation but frequently are no longer required. CT scanning can be particularly valuable when a projectile is suspected to traverse the mediastinum. Tracks of stab wounds and gunshot wounds can be followed with CT imaging. Though CT imaging has improved our ability to identify injury to the diaphragm, operative examination remains the “gold standard” for this specific component of the evaluation.
TABLE 35-1 THORACIC ORGAN INJURY AS A FRACTION OF ALL BODY TRAUMA | ||||||||||||||||||||||||
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Blunt Chest Injuries
Blunt chest trauma may result from several mechanisms—direct, indirect, compression, contusion, deceleration, or blast. Blast injuries result not only from the inertial impact of the shock wave, but also from decompressive implosion that occurs behind the passing shock wave front. Another important mechanism is “spalling”—the disruption of interfacial tissues that occurs as the passing shock wave front releases energy in transition between tissue and gas. Because of the latter “depth charge” like effect, blast injuries exert disproportionate damage to gas-containing organs, such as the lung.
Blunt chest trauma may involve pneumothorax, neurologic dysfunction, respiratory failure, or cardiovascular instability. The principles underlying our general approach to such problems, which are common across a wide spectrum of critical illness, are detailed elsewhere (see Chapters 8, 34, 24, and 4). The current discussion focuses on those mechanical problems unique to blunt (nonpenetrating) chest injury. Rib fractures, increased intracavitary pressures, and shearing forces are the primary mechanisms producing intrathoracic injury in blunt chest trauma. Abdominal events frequently affect pulmonary and cardiovascular function, and in the trauma context the adominal compartment syndrome (ACS) deserves special attentions.
Rib and Sternal Fractures
During chest trauma, older patients who have inflexible ribs frequently sustain bony fractures that directly injure the lung at its perimeter. By contrast, the increased chest wall flexibility of younger patients tends to allow direct energy transfer to the intrathoracic organs without rib breakage. In young patients, rib disarticulations are more common than rib fractures but result in similar physiological consequences.
Rib fracture, the most common form of thoracic injury, usually occurs in the midchest (ribs 5 to 9) along the posterior axillary line (the point of maximal stress). The uppermost ribs are damaged less frequently because of their intrinsic strength and protection by the shoulder girdle and clavicle. Therefore, fractures of the upper ribs imply a very forceful blow and should raise concern regarding coexisting injury to the major airways or great vessels. On the other hand, the relative suppleness of the lowermost ribs makes them less prone to breakage. For that reason, fracture of the lower ribs (9 to 11) suggests an unusually powerful regional impact and the possibility of concurrent splenic, hepatic, or renal injuries. The number of rib fractures roughly correlates with the force of impact and the risk of serious internal injury and death. The history and clinical examination should raise the suspicion of rib fractures, but even when present, fractures may
not be confirmed by conventional radiographic views. (Initial plain chest radiographs fail to reveal as many as one half of all rib fractures.) Although oblique filming is the traditional approach to subtle fracture detection, three-dimensional reconstruction of a helical (spiral) CT represents current state-of-the-art imaging for such problems.
not be confirmed by conventional radiographic views. (Initial plain chest radiographs fail to reveal as many as one half of all rib fractures.) Although oblique filming is the traditional approach to subtle fracture detection, three-dimensional reconstruction of a helical (spiral) CT represents current state-of-the-art imaging for such problems.
Certain features of the radiograph offer clues to etiology. For example, aligned fractures of multiple ribs (“curbstone fractures”) usually result from striking a sharp edge. “Cough fractures” most frequently involve ribs 6 to 9 in the posterior axillary line. Although cough fractures produce significant pain, they generally are not displaced and therefore are difficult to detect.
Rib fractures often injure adjacent tissues as displaced rib ends or fragments cause lung laceration or contusion, pneumothorax, and hemothorax. Because the intercostal and internal mammary arteries are perfused under systemic pressure, large hemothoraces can occur when these vessels are disrupted by fractures. Pain associated with rib fractures frequently causes splinting, hypoventilation, secretion retention, and atelectasis—complications are minimized by adequate narcotic analgesia, intercostal nerve blocks, or epidermal analgesia. Fractures of multiple ribs at two or more sites may produce a free-floating, unstable section of the chest wall known as a flail segment. Hypoxemia resulting from contusion and hypoventilation is an almost universal consequence. Forceful displacement also may disrupt chondral attachments, producing a flail sternum. Discovery of a flail sternum should raise concern for underlying blunt cardiac injury.
Sternal fracture implies a very forceful blow and usually occurs in high-speed motor vehicle accidents when an unrestrained driver strikes the steering wheel or when automobile shoulder harnesses are used without lap restraints. Complaints of pain and tenderness to palpation are signs indicating that CT of the chest should be obtained. Contemporary CT imaging identifies mediastinal vacular injury and is a valued screening tool along with ultrasound for pericardial fluid collections. Echocardiography is the optimal noninvasive test for delineation of cardiac chamber function and identification of pericardial fluid collections. Occasionally, the diagnosis can be made by palpating a “step” where two sternal segments are askew. Although sternal fracture may precipitate respiratory failure and delay weaning by causing pain and altering chest wall mechanics, its greatest significance lies as a potential marker of associated cardiac and bronchial injuries.
Increased Intracavitary Pressures
Abrupt elevation of intracavitary pressures may rupture any air-filled or fluid-filled structure unbraced for the impact. Leak of orogastric secretions after esophageal rupture may result in mediastinitis or empyema. Alveolar rupture may cause pneumothorax, pneumomediastinum, or pulmonary contusion/hemorrhage. Sudden increases of intra-abdominal pressure (IAP) can rupture the diaphragm, herniating the abdominal contents into the chest. Unprotected by the liver, the left hemidiaphragm is at greater risk. By a similar mechanism, a distended stomach or urinary bladder also may rupture when the chest or abdomen is struck forcefully.
Shearing Forces
To varying degrees, all intrathoracic structures are tethered to adjacent tissues. Consequently, shearing forces produced by differential rates and directions of organ motion may cause visceral or vascular tears. Aortic rupture is the most serious injury produced by this mechanism; however, tracheobronchial disruption also may result from deceleration-induced shearing. Direct blows or rapid deceleration may tear pulmonary microvessels, causing pulmonary contusion. If the leak from these vessels is sufficient to form a discrete fluid collection, a pulmonary hematoma may form.
▪ INITIAL MANAGEMENT OF CHEST TRAUMA
Most chest trauma can be managed with some combination of oxygen, analgesics, fluid replacement, and tube thoracostomy. Thoracotomy is necessary in only 10% to 15% of all cases. Initial therapy should consist of ensuring the ABCs: airway, breathing, and circulation. When patency of the airway, adequacy of ventilatory power, or stability of respiratory drive is uncertain, intubation is indicated. Positive-pressure ventilation is initiated for reduced respiratory drive, unduly labored breathing or hypoxemia, or when pain or profoundly deranged chest wall mechanics prevent adequate spontaneous ventilation. After auscultation of the chest to ensure adequate airflow, a portable chest radiograph should be obtained to search for pneumothorax and intrathoracic vascular injury. The plain chest radiograph is insufficient to rule out major intrathoracic vascular injury, however. CT imaging
has replaced the plain chest radiograph and arteriograhy in this regard. Tension pneumothorax (discussed later) is of particular concern, as the associated intrathoracic pressures not only impede venous return but also compress the contralateral lung. The abdominal compartment syndrome, a problem that is caused by edema of intra-abdominal viscera or retroperitoneal bleeding, often develops toward during the resuscitative phase of management (see following). An ultrasonic survey of vital zones, an extended focused abdominal sonogram for trauma (FAST) that includes the upper abdominal and lower thoracic compartments, pelvic region, and heart, can point to the need for urgent intervention. When it can be undertaken expeditiously and safely, CT adds considerably to the level of diagnostic confidence. When time permits and uncertainty exists, three-dimensional reconstruction of data obtained by volumetric CT scanning can be of particular value in planning therapy. Because patients with chest trauma often have severe extrathoracic injuries as well, careful examination should be performed of the head, spine, and abdomen looking for associated trauma. Spine data can be obtained from torso CT scans.
has replaced the plain chest radiograph and arteriograhy in this regard. Tension pneumothorax (discussed later) is of particular concern, as the associated intrathoracic pressures not only impede venous return but also compress the contralateral lung. The abdominal compartment syndrome, a problem that is caused by edema of intra-abdominal viscera or retroperitoneal bleeding, often develops toward during the resuscitative phase of management (see following). An ultrasonic survey of vital zones, an extended focused abdominal sonogram for trauma (FAST) that includes the upper abdominal and lower thoracic compartments, pelvic region, and heart, can point to the need for urgent intervention. When it can be undertaken expeditiously and safely, CT adds considerably to the level of diagnostic confidence. When time permits and uncertainty exists, three-dimensional reconstruction of data obtained by volumetric CT scanning can be of particular value in planning therapy. Because patients with chest trauma often have severe extrathoracic injuries as well, careful examination should be performed of the head, spine, and abdomen looking for associated trauma. Spine data can be obtained from torso CT scans.
Although other problems (such as arrhythmia, myocardial infarction, tamponade, or tension pneumothorax) must always be considered, hypotension that occurs immediately after thoracic injury usually is the result of hypovolemia. Therefore, the early insertion of two large-bore peripheral intravenous catheters is highly advisable. At the time of catheter insertion, blood should be obtained for determinations of electrolytes, creatinine, hematocrit, coagulation parameters, toxicologic screening, and blood cross-matching. When surface veins can be cannulated, the need for central venous catheterization is controversial; equivalent or greater volumes of fluid can be infused per unit time through large peripheral catheters, and there is real risk of iatrogenic complications from central line placement in the busy setting of the trauma suite. Hypovolemia can result from injury to low-pressure (pulmonary or systemic veins) or to high-pressure systemic vessels. Bleeding from veins often will subside spontaneously, whereas arterial disruption usually requires open surgical intervention or, in selected cases, endovascular stent repair. Hypotension is not always the result of hypovolemia; pneumothorax and cardiac tamponade cause hypotension, partly by impeding the return of venous blood to the heart. Hence, constant vigilance for the development of neck vein distension or a quiet hemithorax must be maintained.
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